Redispersible polymer powder on the crack resistance of mortar?

Redispersible polymer powder (RDP) is an important polymer modified material commonly used in modern building mortar, which has a significant effect on improving the crack resistance of mortar. Since mortar is often affected by volume changes, temperature and humidity fluctuations and external loads during hardening and use, shrinkage cracks and structural cracks are prone to occur, affecting the quality and durability of the project. RDP is a powdered emulsion made by spray drying a polymer. After contacting with water, it can be quickly redispersed to form a stable emulsion, giving the mortar excellent flexibility, adhesion and crack resistance. The following is an analysis from the aspects of mechanism, influencing factors, and application effects.

The main cause of mortar cracking

Mortar cracking is mainly caused by factors such as plastic shrinkage, drying shrinkage, temperature stress and structural deformation. Ordinary cement mortar has high brittleness and low tensile strength after hardening. It is easy to crack when encountering matrix shrinkage, external force or temperature change. In addition, poor bonding between mortar and substrate will also form interfacial cracks. To solve this problem, it is necessary to improve the flexibility of mortar, reduce shrinkage stress and enhance bonding ability, and RDP is the key material that plays a role in these aspects.

Mechanism of Redispersible polymer powder to improve the crack resistance of mortar

RDP plays the role of organic polymer modification in mortar, and its main mechanism for improving crack resistance is as follows:

Flexibility enhancement: RDP forms a continuous polymer film inside the hardened mortar, improves the brittleness of the mortar, improves its toughness and deformation resistance, thereby better releasing shrinkage stress and reducing cracks caused by stress concentration.

Adhesion enhancement: The latex powder film enhances the interfacial bonding between the mortar and the substrate and aggregate, effectively preventing interface cracking and improving the overall structural integrity.

Shrinkage stress relief: The polymer has a low elastic modulus, which can disperse and absorb the stress caused by drying shrinkage and temperature difference shrinkage, and reduce the accumulation of tensile stress inside the mortar.

Self-healing effect of microcracks: After RDP forms a film, it can close microcracks to a certain extent, delay crack expansion, and improve the durability of mortar.

Improving pore structure: RDP can optimize the internal pore distribution of mortar, reduce porosity and capillary water absorption, reduce drying shrinkage, and thus reduce the risk of cracking caused by uneven water loss.

Factors affecting the anti-cracking effect

The anti-cracking effect of RDP is affected by many factors:

Dosage: The dosage of latex powder has a significant effect on the anti-cracking performance. Generally, it is appropriate to be 2% to 6% of the mass of the cementitious material. Too little is difficult to form an effective polymer network, and too much may reduce the strength and heat resistance of the mortar.

Polymer type: Commonly used RDP is mainly ethylene-vinyl acetate (VAE) and styrene-acrylate (SAE). Different polymers have different glass transition temperatures (Tg) and flexibility, and they are suitable for different anti-cracking requirements.

Water-cement ratio and construction conditions: A suitable water-cement ratio helps RDP to fully form a film; a good maintenance environment after construction can ensure that the polymer network is fully formed, thereby maximizing the anti-cracking effect.

Synergistic effect with other admixtures: Combined with cellulose ether, toughening fiber, water retaining agent, etc., it can further improve the anti-cracking and construction performance of mortar.

Application effect and typical examples

Tile adhesive and interface mortar: RDP improves the flexibility and bonding strength of tile adhesive, effectively resists thermal expansion and contraction and stress deformation of the substrate, and reduces hollowing and cracking.

Plaster mortar and leveling layer: Adding RDP to plaster mortar can significantly reduce shrinkage cracks and improve the overall crack resistance and durability of large-area plaster layers.

Self-leveling mortar: RDP enhances the toughness of self-leveling mortar, reduces cracks caused by temperature and humidity changes, and improves construction safety and service life.

Insulation system: In the external wall insulation system, RDP-modified anti-cracking mortar can effectively resist the cracking of the external wall caused by thermal stress and wind load, and ensure the integrity of the insulation layer.

Development trends and precautions

With the increasing requirements for building energy conservation and durability, RDP is increasingly used in anti-cracking mortar. In the future, environmentally friendly RDP with low Tg and high flexibility will be more popular. At the same time, it should be noted that the price of RDP is relatively high, and the dosage should be economically optimized in combination with engineering requirements. In addition, construction maintenance management should not be ignored, otherwise the anti-cracking effect of latex powder will be weakened.

Redispersible polymer powder significantly improves the anti-cracking performance of mortar by improving the flexibility, adhesion and internal structural stability of mortar, and is an important modified material for improving the performance of modern mortar. Under the conditions of reasonable proportion and scientific construction, RDP can effectively extend the service life of mortar, improve engineering quality and durability, and meet the needs of high-standard buildings for crack resistance.